1. Field of the Invention
The present invention relates to an ignition coil used for generating a spark between a pair of electrodes in a spark plug in an engine.
2. Description of Related Art
In an engine in which gasoline, for example, is combusted, an ignition coil is attached to a spark plug that is arranged in a combustion chamber of each cylinder in a cylinder head. A spark is generated by the ignition coil between a pair of electrodes in the spark plug, and a fuel/air mixture of gas and air introduced into the combustion chamber is ignited. In a case where a coil part of the ignition coil is inserted in a plug hole of the engine, ozone gas caused due to high voltage, and the like, are generated in the plug hole. Accordingly, in order to ventilate the ozone gas in the plug hole using outside air that is outside the plug hole, a ventilation passage is formed in the ignition coil.
In the engine, pressure in the plug hole has a negative pressure when gas in the plug hole is cooled in a process, in which the engine is cooled from a state in which the engine is warmed up. Meanwhile, when the ignition coil is exposed to water, the water may enter into the plug hole through the ventilation passage Consequently, in order to prevent the water from entering into the plug hole, the formation of the ventilation passage is devised in a seal rubber or the like, which is disposed between the ignition coil and an opening of the plug hole.
There is an ignition coil for an internal combustion engines disclosed in JP9-158820A corresponding to U.S. Pat. No. 5,771,870, as an example of the ignition coil (ignition system) in which the formation of the ventilation passage is devised. The above ignition coil is used with its cylindrical portion inserted into a plug hole formed in the engine and attached to a spark plug disposed in the plug hole, and with its head region disposed outside the plug hole. An annular sealing member (seal rubber) for sealing an upper part of the plug hole is arranged between the head portion and an engine head cover. An axial direction passage, through which the inside of the plug hole communicates with the outside, is formed in the head portion and the sealing member. Furthermore, a radial direction groove is formed to communicate with the axial direction passage, and the radial direction groove is covered with a cap, whereby water accumulated on the engine head cover is prevented from entering into the plug hole. Additionally, in an ignition coil disclosed in JP2006-179824A, a cylindrical portion (coil part) equipped with a primary coil and a secondary coil is inserted in an insertion retention opening of its connector case part through a cylindrical insertion component.
However, in the ignition coil in which the coil part is inserted in the connector case part, further devices are needed to prevent more effectively water or the like from entering into the plug hole using a simple structure.